This invention relates to radar receiver protectors and in particular to improvements in the plasma limiter stage of such devices.
Receiver protecting in radar systems is commonly accomplished by a device that functions as a high power limiter during the time when the radar is transmitting high power bursts. It prevents the power reflected toward the receiver from the radar antennas from burning out the receiver. When the transmitter burst ceases the radar waits for the weak echo from the target. The weak echo is received by the antenna and passes through the receiver protector. Structurally the receiver protector usually includes a high power vial stage, a medium power plasma stage and a diode low power stage.
The plasma stage of state of the art receiver protectors comprises a section of transmit/receive transmission line that is sealed off by microwave windows and contains a soft fill gas. The soft fill gas is converted to plasma for short circuiting the transmission line by means of a radio active ignitor.
While these state of the art receiver protector components have performed satisfactorily in the past, they suffer from various deficiencies. Furthermore, new advanced applications require performance beyond their capabilities. In particular, soft fill gases suffer from long recovery periods, the radioactive ignitor is undesirable, and special metals, such as Kovar are required for matching expansion coefficients to the microwave windows.
By way of example, one particular receiver protector application that requires performance beyond the capabilities of these prior art devices is found in the new Air Force F16 radar system. The advanced F16 radar system differs from the early F16 radar in the critical area of operating PRF's. The advanced F16 radar employs a duty cycle which is 25 times higher than the early F16 radar. The prior art receiver protector has a 0.7 .mu.sec recovery period. If this receiver protector is used and the high duty cycle of the new advanced F16 system, its recovery time would be over 1 .mu.sec. This would result in a significant loss of receiver sensitivity since recovery would encompass a major portion of the receiver listening time.
The present invention is directed toward providing a receiver protector that overcomes the deficencies of prior art devices and that avoids receiver degradation resulting from slow recovery time.